RQC Seminar

299th RQC Seminar

• Speaker

  Prof. Hossein Sadeghpour
  ( Harvard University (ITAMP) )

• Date

  16:00-17:00, (4:00 p.m.- 5:00 p.m.) Wednesday, August 12, 2026

• Venue

  Hybrid( Zoom,
  345-347 Seminar Room, 3F, Main Research Building, Wako Campus / 和光地区 研究本館3階 セミナー室 (345-347) (C01))

• Title

  Imaginary time evolution and ground state preparation using unitary multi-copy protocols

• Inquiries

  norilab_rqc_assist[at]ml.riken.jp

Abstract
Preparing low-energy states of quantum systems is a central goal in quantum science, since these states determine many of the physical and chemical properties of molecules, materials, and many-body systems. They also play an important role in quantum computation and optimization. A powerful theoretical method to reach such states is imaginary-time evolution, which acts like a cooling scheme: it suppresses high-energy components of a quantum state and enhances the low-energy ones. The difficulty is that imaginary-time evolution is not manifestly a unitary process, and therefore hard to directly implement as ordinary quantum dynamics.
In this work, we show how to approximate imaginary-time evolution using only unitary operations, by working with several identical copies of the same quantum system. The key idea is to couple pairs of copies through SWAP-based operations while also using real-time evolution under the target Hamiltonian. Each such step cools one copy and heats the other, therefore arranging many copies in suitable circuits allows one selected copy to approach the ground state, or to acquire a finite temperature scale. We analyze two circuit architectures.

A tree construction guarantees analytic convergence at the cost of many copies, while a more compact hedge construction uses far fewer copies and performs well in numerical simulations. We show that post-selection can substantially accelerate the cooling protocol with practical success probabilities.
These results provide a new route toward ground-state preparation that is naturally suited for platforms where controllable real-time evolution on multiple copies and controlled SWAP operations are available.